Of the various types of nibbling tools now available, there are those which may be classified as internal die carriers in which a punch pushes the metal against a sharp die positioned beneath the sheet metal to be cut. The tool comprising the punch and die is stationary, the sheet being moved along between the punch and die as nibbling progresses. Representative of such type of nibbling tools is the U.S. Pat. No. 3,958,479, to Leibinger issued May 25, 1976. Nibbling is accomplished in these tools by downward motion of the punch against the underlying die.
The art has also developed types of hand-held nibbling tools. Some of these, such as represented by U.S. Pat. No. 2,888,744 to Yermish issued June 2, 1959, have the nibbling die positioned beneath the sheet metal to be cut and operate upon the downstroke of the punch against the die. This type of tool, however, requires either that the nibbling action begin at an open edge of the sheet, or that a large opening be made in the sheet sufficient to accommodate the attached die.
A still further development in the art appears in U.S. Pat. No. 3,861,037 issued Jan. 21, 1975 to Smith et al. This nibbling tool operates on upward movement of the punch against the die positioned at the lower end of the tool, and permits start of the nibbling action in the center of a sheet solely by providing a small opening sufficient to receive the punch. The present invention is an improvement in the type of nibbling tool represented by said U.S. Pat. No. 3,861,037.